Synthesis and Characterization of Linear and Tri-Block PLLA–PEG–PLLA Blends

This study was conducted to synthesize poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) triblock copolymer (PEGLA) with different poly(L-lactide) block length, and explore its applicability in a blend with linear poly(L-lactide) (3051D NatureWorks) with the intention of improving heat seal and adhesion properties at extrusion coating on paperboard. Poly(L-lactide)–poly(ethylene glycol)–poly(L-lactide) was obtained by ring opening polymerization of L-lactide using poly(ethylene glycol) (molecular weight 6000 g mol^?1) as an initiator and stannous octoate as catalyst. The structures of the PEGLAs were characterized by proton nuclear magnetic resonance spectroscopy. The melt flow and thermal properties of all PEGLAs and their blends were evaluated using dynamic rheology and differential scanning calorimeter. All blends containing 10 wt% of PEGLAs displayed similar zero shear viscosities to neat poly(L-lactide), while blends containing 30 wt% of PEGLAs showed slightly higher zero shear viscosity. However, all blends displayed higher shear thinning and increased melt elasticity (based on tan δ). No major changes in thermal properties were distinguished from differential scanning calorimetric studies. High molecular weight PEGLAs could be used in extrusion coating with 3051D without problems.     

Blends of linear and peroxide‐modified branched polylactide for extrusion coating

The purpose of the present work was to improve melt rheological properties of linear poly(L‐lactide) (PLLA) by melt blending with peroxide‐modified branched PLLA for extrusion coating. Peroxide‐modified PLLA, ie, PLLA melt extruded with 0.3 wt% of tert‐Butyl‐peroxybenzoate (TBPB); 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (Lupersol 101 [LOL1]); and benzoyl peroxide was added to linear PLLA in ratios of 5, 15, and 30 wt%. All blends showed increased zero shear viscosity, elastic feature (storage modulus, decreased tan delta), and shear sensitivity. The blends' properties were mostly dependent on the peroxide applied for the modification and, to some extent, on the amount of added peroxide‐modified PLLA. Rheological models suggest that all blend compositions are mainly immiscible. Thermal properties were unchanged; all materials remained amorphous, though the enthalpy of cold crystallization was slightly increased. Extrusion coating on paperboard was conducted with PLLA and peroxide‐modified PLLA blends (90:10). All blends were processable; however, only that made with 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (LOL1) afforded a smooth high‐quality coating surface with improved line speed. Adhesion levels between fibre and plastic and heat seal performance were marginally reduced compared with pure PLLA (3051D). The water vapour transmission measurements with 2,5‐dimethyl‐2,5‐(tert‐butylperoxy)‐hexane (LOL1) showed acceptable water transmission levels, being only slightly higher than for neat PLLA coating.     

Utilisation of continuous atomic layer deposition process for barrier enhancement of extrusion-coated paper

The feasibility of a novel continuous atomic layer deposition process in improving the barrier properties of extrusion-coated papers was investigated. The polymer coatings on paper were low-density polyethylene, polypropylene, polyethylene terephtalate and polylactide. The new method was tested by depositing 100 nm aluminium oxide layers on the polymer side of the structures. According to test results, the aluminium oxide layer produced significant barrier improvements. The water vapour and oxygen transmission rates measured were approximately 3-5 times lower than those of the untreated samples. Even better improvements were found for the water vapour transmission rates of polyethylene terephtalate and polylactide coated papers being over 10 times lower than for the untreated structures. It is proposed that the better water vapour barrier improvements were found because of these polymers' disposition to water sorption in the non-processed samples. The continuous atomic layer deposition process caused also considerable changes in the topography and morphology of some polymers, which reduced the barrier properties and applicability of the structures. Further research is needed to enable the use of lower process temperatures in the continuous atomic layer deposition process, which would improve the feasibility of the new method.     

The dependence of tear behaviour on the microstructure of biaxially drawn polyester film

The structure-property relationship between a biaxially oriented film from poly(ethylene terephthalate) and its fracture behaviour measured using the Trouser Tear method, has been explored. X-ray diffraction (XRD) was used to characterise the orientation distribution of crystalline and non-crystalline material in the plane of the film and compared with the fracture energy, G _c measured in four directions during tearing. The fracture energy averaged over the four directions ranged between 12 and 25 kJ m^–2, and was found to correlate closely to the draw ratio during manufacture and therefore the degree of molecular orientation. However the individual values of G _c displayed a further level of complexity.The expected anisotropic character of the fracture energy was found to change systematically as a function of position across the original width of manufactured film. This feature compared well with the underlying, crystalline orientation distribution and provided strong evidence that under the mode III deformation of the tear test, the fracture mechanism involves the amorphous-crystallite surface boundary.Further support for this mechanism was provided by a simple model which, based on this assumption was shown to predict reliably, the anisotropic character of the film.     

The Effect of Flame Treatment on Surface Properties and Heat Sealability of Low‐Density Polyethylene Coating

The target of this study is to investigate the correlation between surface properties and heat sealability of flame‐treated low‐density polyethylene (LDPE) coating because it is vital to know how to modify the surface properties of LDPE coating without losing the heat sealing properties. Flame treatment showed a significant effect on the heat sealing properties of LDPE‐coated paper. For example, the heat sealing temperature of LDPE coating decreased or alternatively doubled, depending on the equivalence ratio (air–propane ratio) of flame treatment. In addition, the hot tack strength was significantly enhanced by flame treatment, which broadened the hot tack window of LDPE‐coated paper. The reason for the heat sealing performance of flame‐treated LDPE coating was believed to be related to the simultaneous reactions, that is, cross‐linking and chain scission, occurring on the LDPE surface. The molecular weight of LDPE surface increased or decreased, depending on the dominating reaction during flame treatment. This affected the chain mobility and the amount of chain interdiffusion across the seal interface and finally defined the heat sealing performance of LDPE‐coated paper. Copyright © 2012 John Wiley & Sons, Ltd.     

Characteristics of nFOG,an aerosol-based wet thin film coating technique

An atmospheric pressure aerosol-based wet thin film coating technique called the nFOG is characterized and applied in polymer film coatings. In the nFOG, a fog of droplets is formed by two air-assist atomizers oriented toward each other inside a deposition chamber. The droplets settle gravitationally and deposit on a substrate, forming a wet film. In this study, the continuous deposition mode of the nFOG is explored. We determined the size distribution of water droplets inside the chamber in a wide side range of 0.1–100 µm and on the substrate using aerosol measurement instruments and optical microscopy, respectively. The droplet size distribution was found to be bimodal with droplets of approximately 30–50 µm contributing the most to the mass of the formed wet film. The complementary measurement methods allow us to estimate the role of different droplet deposition mechanisms. The obtained results suggest that the deposition velocity of the droplets is lower than the calculated terminal settling velocity, likely due to the flow fields inside the chamber. Furthermore, the mass flux of the droplets onto the substrate is determined to be in the order of 1 g/m³s, corresponding to a wet film growth rate of 1 µm/s. Finally, the nFOG technique is demonstrated by preparing polymer films with thicknesses in the range of approximately 0.1–20 µm.     

Development of superhydrophobic coating on paperboard surface using the Liquid Flame Spray

This paper introduces a new method for generating nanoscale coatings in a continuous roll-to-roll process at normal pressure. Nanostructured and transparent coating, based on titanium dioxide nanoparticles, was successfully deposited on-line at atmospheric conditions on pigment coated paperboard using a thermal spray method called the Liquid Flame Spray (LFS). The LFS coating process is described and the influences of process parameters on coating quality are discussed. Nanocoating was investigated by a field emission gun scanning electron microscope (FEG-SEM), an atomic force microscope (AFM), an X-ray photoelectron spectroscopy (XPS) and a water contact angle measurement.The highest measured water contact angles on the nanocoated paperboard surface were over 160°. Falling water droplets were able to bounce off the surface, which is illustrated by high speed video system images. Regardless of the high hydrophobicity, the coating showed sticky nature, creating a high adhesion to water droplets immediately as the motion of the droplets stopped. Nanocoating with full coverage of the substrate was produced at line speeds up to 150 m/min. Therefore, the LFS coating has scale up potential to industrial level as an affordable and efficient method for coating large volumes at high line speeds.     

Superhydrophobic Coatings on Cellulose‐Based Materials: Fabrication,Properties, and Applications

Wettability of a solid surface by a liquid plays an important role in several phenomena and applications, for example in adhesion, printing, and self‐cleaning. In particular, wetting of rough surfaces has attracted great scientific interest in recent decades. Superhydrophobic surfaces, which possess extraordinary water repelling properties due to their low surface energy and specific nanometer‐ and micrometer‐scale roughness, are of particular interest due to the great variety of potential applications ranging from self‐cleaning surfaces to microfluidic devices. In recent years, the potential of superhydrophobic cellulose‐based materials in the function of smart devices and functional clothing has been recognized, and in the past few years cellulose‐based materials have established themselves among the most frequently used substrates for superhydrophobic coatings. In this Review, over 40 different approaches to fabricate superhydrophobic coatings on cellulose‐based materials are discussed in detail. In addition to the anti‐wetting properties of the coatings, particular attention is paid to coating durability and other incorporated functionalities such as gas permeability, transparency, UV‐shielding, photoactivity, and self‐healing properties. Potential applications for the superhydrophobic cellulose‐based materials range from water‐ and stain‐repellent, self‐cleaning and breathable clothing to cheap and disposable lab‐on‐a‐chip devices made from renewable sources with reduced material consumption.     

Compressibility of porous TiO2 nanoparticle coating on paperboard

Compressibility of liquid flame spray-deposited porous TiO₂ nanoparticle coating was studied on paperboard samples using a traditional calendering technique in which the paperboard is compressed between a metal and polymer roll. Surface superhydrophobicity is lost due to a smoothening effect when the number of successive calendering cycles is increased. Field emission scanning electron microscope surface and cross‒sectional images support the atomic force microscope roughness analysis that shows a significant compressibility of the deposited TiO₂ nanoparticle coating with decrease in the surface roughness and nanoscale porosity under external pressure.

PACS

61.46.-w; 68.08.Bc; 81.07.-b